It is important to maintain the cold chain for frozen vegetables from the factory to the consuming household or institution. Sometimes this is undesirable or impossible. In such case, the vegetables may be canned, to preserve the food value.
One instance where this is case is where frozen vegetables are purchased in bulk in a tropical climate and refrigeration is costly or impossible. In such case, the frozen vegetables are thawed and canned.
Another instance where this is the case is in the production of canned mixed vegetables. These cannot be produced from fresh vegetables because of the different crop months for the various vegetable constituents. For example, carrots are harvested in October, November and December, whereas green peas are harvested in June through mid-July and green beans are harvested from late July through early October. To produce canned mixed vegetables, the various vegetables for the mix are frozen in the season of harvest and then are mixed, and the mix of frozen vegetables is thawed and canned.
Another instance where this is the case is in the year-round production of canned stews and other thermally sterilized food preparations in which vegetables are one of the ingredients. The vegetable ingredients are obtained by thawing frozen vegetables as needed for stew or other thermally sterilized food preparation and canning.
Still another instance where this is the case is production of canned vegetables for the U.S. military. U.S. Army Procurement routinely buys frozen vegetables and thaws them and packs them in tray cans which contain 61/2 to 7 pounds of product and which are opened for serving out of the tray.
It is known to use a low-temperature blanch to increase vegetable firmness prior to a higher temperature blanch to deactivate peroxidase to prevent off flavor generation in the production of frozen vegetables. See Canet, W. et al., International Journal of Food Science and Technology, 22, 273-277 (1987) and Bengtsson et al., U.S. Pat. No. 4,521,439. Moreover Lee, C. Y. et al., Journal of Food Quality 11, 279-287 (1988) provides results of an investigation of the effects of different blanching conditions on residual enzyme activities and quality changes in green beans during frozen storage. Moreover, the parent applications herein are directed to utilizing a low temperature blanch to increase the firmness of canned vegetables. However, there appears to have been no work prior to the invention herein on blanching conditions that are advantageous for vegetables which are frozen before canning.